Managing heat stress in propagation

Summer is a busy time of year for perennial growers. Creeping Phlox, Iberis, Dianthus and others have to be propagated this time of year in order to ship to customers for growing and bulking before overwintering. Unfortunately, Summer can be a very challenging environment for rooting perennials with the relentless heat and oppressive humidity. This stress can take its toll and affect the percentage and uniformity of rooting. Here’s a few tips, by Chris Fifo Product Representative at Darwin Perennials, for avoiding Summer pitfalls:

Reduce your greenhouse temperature any way possible

  • Increase your percentage of shade. Add two layers if necessary.
  • Shade the entire house, not just over the propagation area.
  • Use white shade cloth! This stays cooler than black. Plus it is brighter so your crop does not starve for light.
  • Do whatever you can to increase passive cooling like rolling up greenhouse sides or opening up roofs.
  • Use evaporative cooling such as fan and pads or fog.
  • Water down the floors and empty benches throughout the day to remove the heat and increase humidity.

Watch the amount of mist you are using on your URCs. Avoid media becoming saturated, which can significantly delay rooting and cause losses.

  • Ideally, media moisture should begin at a "4" and end at a "4" or slightly less.
  • Reduce air flow (proportional to amount of shade) in the prop house to increase humidity and decrease amount of mist needed.
  • Use tenting with white plastic and shade cloth if appropriate for the crop.
  • Use a very fine mist nozzle. The goal is to wet the leaves, not the media.
  • Only run the mist as often as necessary for the crop. Try to keep older crops (day 7ish) and newer crops separate as they have separate requirements.
  • An increased amount of medium grade perlite (not coarse) in the media can help with a tendency for over-misting.
  • Use proper IBA and Pagaent applications to hasten rooting and get the trays out of mist as quickly as possible.

Manage fungus gnats and shore flies in propagation. Larvae will thrive in the hot, wet environment and feed on young roots or bore into the stems of URC.

  • Use yellow or blue sticky cards to evaluate if adult numbers are going up or down.Have a standard number of cards per area, such as one card/1,000 ft2
  • Count the cards weekly and graph the numbers.
  • Change the cards weekly!
  • Use biologicals or insect growth regulators to manage the larvae population.
  • Rolls of sticky tape for mass trapping are also very useful.
  • Imagine if each adult on this sticky tape lays 100 eggs in its life cycle.

For more information:
Darwin Perennials
622 Town Road
West Chicago, Illinois 60185-2698
630 231-3600

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